Petroleum heater



Augu l0, w43. F. H. PRAEGER PETROLEUM HEATER Filed sept: 22, 1941 llNvENToR. BY fv/QNX /Qe/Qf'e ATTORNEY.

Patentecl Aug. 10, 1943 UNITED STATES PATENT OFFICE PETROLEUM HEATERFrank H. Praeger, Merton, Pa., assigner to Alcorn Combustion Company,Philadelphia, Pa., a corporation o! Delaware Application september 22,1941, serial No. 411,890

. 7 claims. (ci. 122-356) My invention relates to heating systems, moreparticularly to heaters especially designed for the heating of petroleumand its components and has for an object the Provision of a heater ofhigh efliciency and of relatively low cost.

It is a. further object of my invention materially and substantially toincrease the heat absorption in that zone of the heater generally knownas the convection chamber.

It is a further object of my invention to so increase the transfer ofheat within the convection chamber to the oil A:flowing through thetubes therein that the present normal size of the convection chamber maybe decreased to a substantial degree without loss in heater eflifciency;or. with the present, normal size of convection chamber materially andsubstantially to increase the efficiency of the heater byproviding for agreater absorption of heat in the con vection section.

In many petroleum heatershot gases or the l products of combustion ilowfrom a nre chamber into a convection section where the transfer oi! heatfrom the hot gases to the oil is largely by convection. Usually theconvection section consists of a relatively large number of tubesintimately washed by the gases and through which tubes heat is conductedto the oil iiowing therein. In general, the spacing of the tubes onefrom the other is limited by the temperature and pressure conditionswithin the convection section and while a closer spacing may sometimesbe desired, the return bends, headers, or fittings are not available forsuch-closer spacing of the tubes- Moreover, tubes in the convectionsection are located equal distances one from the other because with thisarrangement maximum room for the headers is provided for the minimumspacing between tubes. Nevertheless the gases passing between adjacenttubes divide around the next tube so that the gas velocity is reduced asmuch as fty per cent in the region where the divided flow occurs.

It is a further object of my invention to provide means for maintainingthroughout the convection bank and ,in the regions of divided ow,substantially constant and relatively high, the velocity of the hotgases for the more effective heating of the convection tubes.

In the past there have been many proposals for increasing the transferof heat in the convection section. YFor example, it has been proposed toencircle :the oil conducting tubes with gill rings or especially madecastings. Hairpinlike members and refractories secured to the tubes havebeen suggested to increase the absorption of heat. These schemes allinclude the disadvantage of the interposition of a substantial amount ofheat insulation between 'the gases and the tubes.

In carrying out my invention in one form thereof, I provide means spacedfrom the convection tubes for directing and controlling the ow of gasesthereover to insure a high velocity of the gases over the tube surfacesand to overcome and prevent large decreases in the velocity of thecombustion gases passing through the convection section. Morespeciically, I provide members extending lengthwise or longitudinally ofthe convection tubes and in spaced relation therewith and so positionedas to provide narrow passages between each member and two adjacent tubesso that upon division of the gases between a pair ofl tubes the area ofthe ow passages will be reduced by one-half, thereby to prevent materialreduction in the velocity oi the gases.

For a more complete understanding of my invention, reference should bemade to the accompanying drawing wherein I have shown in Fig. 1 asectional elevation of a heater embodying my invention;

Fig. 2 is an enlarged fractional elevation of a pat of one of theconvection sections of Fig. 1; an

Fig. 3 is a fractional side elevation showing the tube sheets in theleft hand convection section of Fig. 1.

Referring to the drawing, I have shown my invention in one form asapplied to a petroleum heater of the type which forms the subject matterof a copending application, Case No. AC23, Serial Number 411,891, filedconcurrently herewith by Roy S. Lyster and assigned -to the sameassi-gnee as the present invention and comprising three fire chambersI0, vI I, and I2. Suitable fuel, such as oil or gas, is burned withinthe respective re chambers. By means of a pluralit'yoi burners I4, eachdirecting oil or gas within muilles I5. spaced along a front wall I6 ofthe-heater, burning gases are projected generally horizontally acrossthe lire chamber I0 and intermediate a bank of floor tubes I1 and a bankof roof tubes I8. 'I'he door tubes are located adjacent the iioor I9while the bank of roof tubes I8 slopes upwardly along the upwardlysloping roof' 2li of lire chamber I0. The hot gases and products ofcombustion -rise through a convection section 2| of the heater and thenpass into a second convection section 22. The rows of tubes in eachconvection section are in staggered relation to each other.

The ilre chamber I2 is of the same construcnected in parallel with eachother by means of large headers (not shown) Fuel is burned above the oortubes 26 and is preferably directed inwardly from opposite ends of theheater and lengthwise of the door tubes 26, three of such burners 23being shownv in the drawing, the outer two burners being for gas and thecenter burner for oil.

The combined gases and products of combustion from the fire chambers I0,II,and I2 unite within the common convection section 22 and afterpassage therethrough flow to the stack (not shown).

My invention, applicable to any kind of a convection section whetherup-draft or downdraft, may be readily understood by reference to theenlarged fractional view of the convection section 2|,y shown in Fig. 2.More particularly, the hot gases `or products of combustion from burnersI4 pass through the lowermost row of four tubes which are, of course,subjected to radiant heat fromthe lire chamber I0 and to convectionheating by the gases contacting them. There are three openings betweenthe tubes, not counting the opening to the left of the tube 29 and theopening to the right of the tube 30. Since the tubes in the rst rowincluding tubes 29 and 30 are subjected to both radiant and convectionheat,'no provisions are made to increase the rate of convective transferin the regions of divided flow of the gases. Some heat by, directradiation is also received by the second row of tubes, 3I-34, and noprovision has been made to increase the convective transfer thereto inthe regions of divided gas flow.

My invention is shown applied intermediate the second row of'tubes 3I-34and the third row of tubes 35--3'I, in the manner now to be explained.The gases rising between the adjacent tubes 3I-32 divide, one partflowing to the left around tube 35, and the other part flowing to theright thereof. As a result of this division, the velocity normally wouldbe 'reduced one-half in the regions of divided flow and heat would betransferred at low rate to the heat-absorbing tubes 3I, 32, and 35.`However, by interposing suitable means, such for example as flowcontrolling elements 38 and 33 in the regions of divided flow, the gaspassagesmay be reduced in area to prevent reduction in the rate of flowof the gases. The rate of heat transfer is maintained at a higher ratedue to the continued high velocity of the convection gases. Similarly,the gases flowing between the tubes 32--33 divide, one-half going to theleft of tube 36 and Vone-half to the right. of it. The flow-controllingelements 39 v and 40 reduce the now areas to prevent decreased velocityof the gases in contact with the tubes 32, 33, and 36, and the elements40-43 perform like functions for the tubes 32-34 and 36-31. The gaseswhich flow between the tubes 35 and 33 are about the same in quantity asthe gases which flow between tubes 3l and 32, or as between tubes 32 and33. In consequence, the means for controlling the flow of the gases areomitted from between tubes 3I-34 and 35-31 but they are included, 44-48,in the regions of divided ow just above tubes 35-3`L The additional owcontrolling means 52--55 are likewise disposed in the regions of dividedow just below tubes 56 and 51 and above tubes 49-5I.- All of the tubesin the convection section 2| are in staggered relation. They areequidistant one from the other and lines drawn between the respectivecenters form equilateral triangles, as shown by the broken-line trianglebetween the centers of tubes 32, 33 and 36.

In the preferred form of my invention, the iiow controllingmeans isdisposed intermediate the sides of such equilateral triangles, theelements 40 and 4I having such positions. While neither the shape northe material of which the flow controlling means is made is deemed anessential part of my invention, I prefer to use cast iron tubes or steelpipe of the requisite size, although it is again emphasized solid barsof heat-refractory material, either circular, polygonal, or angular inshape, may be used. In the drawing solid bars are shown. When there issubstantial spacing of certain tubes from an adjacent wall, it isdesirable to provide a projection such as the projection 24a, whichextends outwardly from the bridge wall 24, to prevent by-pass of thegases through the opening between tube 3l and the plane of the bridgewall 24.

Again referring to tubes 32 and 33, it is, to be observed the elements40 and 4I not only reduce the area of the iiow passages in the regionsof divided flow but they also'direct the gases against the adjacentheat-absorbing surfaces of tubes 32, 33, and 36 in contrast with theheat-insulating material which has in the past encircled convectiontubes. By maintaining the velocity of the gases over the tube surfacesand over a greater area thereof the rate of heat absorption byconvection is increased materially. l

The initial spacing of the tubes in the convection section is ordinarilydetermined by the design of the headers. The manufacturers of suchheaders have adopted standard designs with predetermined distancesbetween tubes, although such distances vary with the temperature andpressure of the oil being heated. For low pressure, low temperatureoperation, the tubes may be spaced closer together than for the highertemperatures and pressures. The greater spacings are required to allowfor increased thickness of the metal in the headers or return bends forthe higher temperatures and pressures. That is, the headers are made foras close aspacing as each design permits (about one-half a tubediameter) and for higher temperatures the tube spacing must be increasedfor the heavier headers which must be used.

It will be seen that regardless of tube spacing,

there will always be a substantial decrease in the velocity of the gasesin the regions of divided flow and that the flow-controlling means willmaintain the velocity of the gases and prevent decrease in the rate ofheat transfer.

Moreover the gases are directed by the elements against the convectiontube surface. This directing effect is important as will be seen byconsidering the flow of gases around a typical tube, the tube 32. Sincethe rising gases pass to the right and the left of tube 32 theintermediate portion is not as thoroughly washed by the gases and theheat transfer thereto is materially less than to the lower sideportions. Since a greater quantity of gases, about twice, ows betweentubes 3I and 32 the maximum transfer rate is along the side portions oftube 32. By reaaround tube 35 are directed against the upper side oftube 32. That is, they must pass between ele- J ment 39 and tube 32; andbetween element l0 and tube 32, the two subdivided streams Joining to.-gether between elements 33 and 40. Thus the gases to substantial degreeencircle tube 32.

The encircling effect is even more pronounced in connection with anothertypical tube 36. In this case,A the gases ow between the respectiveelements 40 and 4| and then divide one part passing between element 40and tube 36 and the other between element 4| and tube 33; in contrastwith the undirected gases which do not so eiectively wash the lowerportion of tube 32. Both sides of .tube 36 are then thoroughly washed bythe gases inthe regions of united iiow of the gases. In the subsequentregions of divided flow, the gases are again directed against the upperhalf of tube 33 because they must pass between element 45 and'tube 36and between element 46 and tube 36. Besides decreasing the area of theow passages to prevent decrease in both gas velocity and rate ofheating, each element directs the gases against two convection tubes.Adjacent elements such as lil-4|, and. 45-46, by their location extendthe effective heat absorbing surface of their associated tubes bysubstantial elimination of the previously relatively low rate areas ofeach tube comprising the upper and lower half of each tube, or the sidesof each tube normal to the flow of gases through the convection section.

While flow controlling elements which maintain the velocity of the gasesare preferred, it is of course apparent that elements which decrease thecross-sectional area of the gas passages inthe regions of divided floware highly benecial because of their gas directing functions even thoughthe original velocity ofthe gases is not maintained. Also if the flowareas are proportionately smaller, the gas velocity may actually exceedthe velocity between adjacent tubes preceding the regions of dividedflow. In each form of my invention the heat transfer rate is maintainedhigh in those regions where it formerly has been exceedingly low. Inconsequence, the convection bank has a high overall eiilciency. l

As above indicated, the temperature and pressure requirements on a sixinch outside diameter tube may require a spacing from the center of onetube to the center of an adjacent tube of from 9 inches to 11 inches ormore, with the result the convective transfer is greatly decreased 'withan eleven inch spacing over what it would be with between tubes 3| and32 but as above explained the now controlling element 38 directs orlocalizes the flow of gases against a greater proportion of theheat-absorbing surfaces of tubes 3| and 35.

In calculating the heat absorbed in a convection section determinationis first made of the K factor defined as the British thermal units persquare foot of heat absorption surface per hour per degreeof temperaturedifference (F.) between the convection gases and the liquid beingheated. In accord with my invention the K factor is increased fromthirty to fifty per cent, which means more heat may be absorbed persquare foot of heat absorption surface. The convection bank is moreefllcient. It may be correspondingly smaller for a given heating duty.

The convection section 2 la, as above stated, including the nowcontrolling elements, is identical with the convection section 2| andneed not be further described.

M y invention has also been applied to the central convection section 22and there are shown rows 60-61 of ow controlling means for the.combustion gases passing therethrough. Though the tubes may be connectedfor any desired sequence of flow, I have shown inlets 69 and 10 forentry of two streams of oil to the convection section 22 from which onestream ows through the tubes 2|a, |8a and Ila of fire chamber I2; andthe other-stream nows through tubes 2|, I8', and |1 of fire chamber |0.-From the respective outlets 1| and 12 the streams may be conducted tovaporizing drums and the oil vapors therefrom may pass throughthe floo'rtubes 26 in flre chamfactor is thirty to fifty per cent greater byreason of the flow-controlling elements, an increase over the K factorof convection sections of the prior my invention, it is to be understoodthat I do not a closer spacing. As a specic example, and not to be takenas limitative in any way with respect to my invention, a 51/2 inchoutside diameter tube maybe spaced 81/2 inches center to center, whichleaves between adjacent tubes an opening of 3 inches. To maintain thesame velocity of the gases in the regions of divided ow, the owcontrolling means should, therefore, if in circular form, have adiameter of 11/2 inches, which leaves on each side thereof a 3A, inchopening between it and the nearest tube; or stated differently, witheach of elements 38-43, 1%/2 inches in diameter, the area of each of thegas passages such as between the element 38 and the tubes 3| and 35 isone-quarter that between tubes 3| and 32. Since half the gases flow tothe left or intermediate tubes 3| and35, the velocity thereof in theregions of divided ilow and in convective contact with tubes 3|-35remains not only about the same as limit myself thereto, since manymodifications may be made, and I, therefore, contemplate by` tion gasesto the tubes of the next row, each tube thereof disposed intermediateone of said inlet passages for divided flow of gases around it, andmeans comprising elongated elements disposed in the regions where thegases divide and each of a size which decreases the areas of theflow-passages an amount adequate to prevent tubes.

rows coinciding with the apices of equilateral triangles, the regioncorresponding with the base of each said triangle forming an inletpassage for now of gases between adjacent tubes of one row, and meansdisposed in spaced relation with said tubes and intermediate the tworemaining sides of each said equilateral triangle for reducing the areaof the ow passage between adjacent tubes and for preventing substantialdecrease in the velocity of the gases in convective contact with saidlast-named tubes.

3. The combination With a heater, of a convection section comprising aplurality of tubes the centers of adjacent groups of three of which.coincide with equilateral triangles, and means interposed intermediateeach row of tubes and intermediate the legs of each said triangle fordefining narrow passages for the ow of combustion gases throughout asubstantial part of the circumference of two of said tubes.

4. In a heater having a convection section consisting of rows of tubeswith the tubes of each row disposed in staggered relation with the tubesof each adjacent row, said staggered arrangement producing divided iicwof gases about a tube in one row after unitedy flow of gases betweenadjacent tubes of the preceding row, means for preventing substantialdecrease in the velocity of iiow of the convection gases within theregions of divided flow comprising elongated elements so disposed as todecrease the area of 1 the ow passages within said regions, and each ofa size so as to produce undiminished flow of the divided gases in thepassages of decreased area and against and in intimate convection heattransfer with the tube surfaces therein.

5. The combination with a heater, of a convection section having aplurality of rows of tubes adjacent groups of three of said tubessubstantially coinciding with the aplces of equilateral triangles,elongated elements disposed intermediate' the legs of said triangles andextending parallel to said tubes and deiining narrow passages for thenow of combustion gases throughout a substantial part of thecircumference of the adjacent tubes, and tube sheets for supporting saidtubes and said elongated elements.

7. The combination with a heater, of a convection section having aplurality of rows of tubes in staggered relation and disposed with theaxes of the tubes of adjacent rows substantially coinciding with theapices of equilateral triangles, the region between adjacent tubes ofone row corresponding with one side of one of said triangles forundivided ow of gases therethrough, and the regions corresponding withthe other two sides of said one of said triangles providing for dividedflow of gases therethrough, and elongated elements extending parallel tothe tubes disposed midway of the regions of divided iiow for reducingthe area of the flow passages between adjacent tubes, thereby to preventsubstantial decrease in the velocity of the gases in said regions ofdivided iiow.

FRANK H. PRAEGER.

